Catalytic hydrogenation of acetophenone to phenyl methyl carbinol



Patented Nov. 20, 1951 CATALYTIC HYDROGENATION F ACETOPHENONE TO PHENYLMETHYL CARBINOL Donald M. Young, Frank G. Young, Jr., and Howard R.Guest, Charleston, W. Va., assignors', by mesne assignments, to UnionCarbide and Carbon Corporation, a corporation of New York No Drawing.

1943, Serial Original application October 14,

No. 506,214, now Patent 2,544,771, dated March 13, 1951. Divided andthis application June 14, 1947, Serial No. 754,770

Claims. (Cl. 260--618) We have discovered a new and useful improvementof the art of catalysis. More particularly, the improvement is of thecatalytic hydrogenation of acetophenone whereby acetophenone, in thepresence of mixed oxides of copper and chromium, is convertedselectively to phenyl carbinol, with good yields and efiiciencies.

That acetophenone may be hydrogenated to form phenyl methyl carbinol iswell known. Phenyl methyl carbinol is important as an intermediate inthe production of styrene. According to one series of reactions, ethylbenzene may be oxidized to acetophenone, acetophenone hydrogenated tophenyl methyl carbinol, and the carbinol dehydrated to styrene. It is tobe noted that in this series of reactions none of the reagents used orby-products formed in the main reactions is of the nature of adifliculty removable impurity which may remain even in traces to affectadversely the quality of the ultimate product, styrene. The onlyby-product is water which is readily separated and, aside from the basematerial undergoing conversion to styrene or an intermediate, the onlyreagents are the readily available, low cost materials, oxygen andhydrogen.

Although, in the reduction of acetophenone by hydrogen, the only productof the main reaction is phenyl methyl carbinol, not all catalysts aresuificiently selective in their action to form the main product to theexclusion of side reaction products. In some instances, the formation ofproducts by side reactions may increase disproportionately with increasein catalytic activity or other conditions resulting in anincreased rateof the main reaction.

Among possible side reaction products are ethyl benzene and cyclohexylmethyl carbinol. In the dehydration of phenyl methyl carbinol tostyrene, any cyclohexyl methyl carbinol present therein would besimultaneously converted to vinyl cyclohexane while any ethyl benzenepresent would pass through unchanged. The boiling points of both vinylcyclohexane and ethyl benzene lie so close to that of styrene that theirsep- .aration from styrene by distillation is not accomplished easily.Although no difliculty is encountered in separating ethyl benzene fromphenyl methyl carbinol in view of the wide difierence in their boilingpoints, a somewhat different situation is presented by the high boilingcyclohexyl methyl carbinol which distills only about 14 0. below phenylmethyl carbinol at normal pressure, with even less difference at reducedpressures. It does not appear, as far as is known, that the importanceof having phenyl methyl 2 carbinol free or" such side reaction productshas heretofore been recognized in the production of high qualitystyrene.

We have discovered that acetophenone may be hydrogenated selectively tophenyl methyl car-- binol to the substantial exclusion of side reactionproducts by carrying out the reaction in the presence of acopper-chromium hydrogenation catalyst in which the proportion ofchromium to copper, calculated on a metal basis, is from 7 to 25 partschromium per 100 parts of copper. The catalyst may conveniently beprepared by roasting a mixture of the carbonates of copper and chromiumto convert them to the oxides. Usually a temperature of about 800 C.maintained for a period of about 20 to minutes is sufficient for thispurpose. The reaction proceeds smoothly, in contrast to the stronglyexothermic decomposition accompanying the preparation of some,

catalysts heretofore proposed, and may be carried out readily on acommercial scale.

In preparing the catalyst, a mixture of copper and chromium carbonatesand basic carbonates suitable for roasting may be obtained, if desired,

by precipitating the carbonates from an aqueous solution of the metalsin the form of such soluble salts as the nitrates, for instance. Theprecipitating agent may be an aqueous solution of a soluble carbonate,for example, ammonium carbonate. and this procedure has the advantagethat the remaining salts formed by the metathesis are water-soluble andeasily washed out from the precipitate. Before converting the mixedcarbonates to the oxides, it may be found desirable to subject thewashed precipitate to a preliminary drying at a temperature of about toC. over a period of 10 to 20 hours approximately.

In carrying out a hydrogenation of acetophenone using the mixture ofblack oxides as first obtained by decomposition of the carbonates, aninduction period may be observed. Where the hydrogenation is to becarried out in a continuous-type process, it may be advantageous to givethe catalyst a preliminary activation. For instance, the catalyst may beactivated by heating it in acetophenone under hydrogen pressure. Othermethods of activation include heating the catalyst in a mixture ofphenyl methyl carbinol and acetophenone at atmospheric pressure under areflux, or with dry ethyl benzene under hydrogen pressure, or in anatmosphere of hydrogen alone. In activating the catalyst, it isdesirable that the heating be carried out at a temperature which isusually about to 200 C., although higher and lower temperatures may alsobe used.

Oxide mixtures in which the copper and chro- 6 mium are present in anamount from about 9 to parts otchromium' per 1033" parts ofcopper aresuperior catalysts "in the hydrogenation'pf acetophenone selectively tophenyl methyl carbin01, and are preferred. Using a catalyst having thispreferred ratio, the hydrogenation not only proceeds at a high rate withnegligible amounts of ring hydrogenation and ethyl benzene formation,but the reaction may also be carried out at temperatures and pressureswhich are low in comparison with those which are commonly" employed inhydrogenation processes generally; and phenyl methyl carbinol isobtained in good yield. The catalyst upon activation gives a maximumrate of hydrogenation which is considerably high er than that attainablewith catalysts outside the preferred range; and retains its maximumactivity over a longer period; The rate cfliydro' genation decreases inthe direction of both lower and higher chromium content outside thepreferred-range but it decreases more sharply in the directionof thelower concentration than the higher. The ease of activation appears toincrease with-increasing chromium content within the limits of thechromium-copper proportions of the present invention; Additionally,catalysts of the preferred proportions may be activated v ithoutbecoming pyrophoric, and these non-pyrophoric activated catalysts havethe advantage that they are less hazardous for large scalecommercial-operations than a pyrophoric catalyst.

The hydrogenation may be carried out at an elevated temperature andunder hydrogen pressure ina conventional pressure reactor. Ingeneral-,-- from about 0.5 to 10 parts of catalyst per 100=parts ofacetophenone are suitable in carrying-out the reaction; but anexcess ofcatalyst is not, of itself, objectionable. Depending largely uponcatalyst concentration the'hydrogenation may'be carried out usinghydrogen'pressures as low as 50 to 100 pounds persquare incha-nd attemperatures ranging from 130 to 175C; Higher pressures and temperaturesmaybe used if desired, but ordinarilyit is unnecessary to resort topressures much'above 150 to 200 poundsper square inch or to temperaturessubstantially higher than 200 C; On the other hand, at temperaturesbelow120 C1, the rate may become too slow' to be practicable. Thehydrogenation may be carried outin a continuous manner by spray ing amixture of the catalyst and acetophenone intd an atmosphere of hydrogenunder suitable pressure, 'using' an'activat'ed catalyst if desired;Thecatalyst may berecovered after the hydrogenationds'complete'd, andreused; It may readilyberactivated, if need be by" procedures includingsteaming'an'd roasting, for instance.

The invention may be further illustrated 'by the following examplesz' ii Example 1 A precipitate of the mixed carbonates of copper and chromiumwas formed by adding an aqueous solution of ammonium carbonatemcnohydrate; (memos-H20, containing 175' grams of the ammonium salt inone'liter of water, to

an aqueous'solution of copper nitratetrihydrate;

minutes, and for minutes thereafter; The "precipitate of mixedcarbonates was separated from the'liquid by filtration and washed with1.5 liters The solution was well tated; over a'period of 20 minutes.

of water. The washed precipitate was then agitated with'two 5 00milliliter streets of water, in succession, each agitation "step beingfollowed by filtration and further washing. The material thus obtainedamounted to 96 grams after it had been dried in an oven at a temperatureof C. for 16 hours. Finally, the dried material was heatedatatemperature of 280 to 300 C. for twenty minutes, after it first hadbeen brought up to'a temperature of 280 C., while being agi- There wasproduced 72 grams of black mixed oxides which were found by analysis tohave a chromium-copper ratio of 13.8 parts chromium to 100 parts coph {rExample 2 To pure acetophenone, 100 parts, contained in asuitablereaction vessel, was added 2 parts by Weight of the black mixedoxides of Example 1 and the mixture thus obtained was heated to about C;Hydrogen wa's'then introduced intothe heated mixture under a pressuremaintained at an average of about 75 pounds per square inch and'themixture agitated continu ously. Under these conditions the oxide mixturewas found to be slowly activated, as indicated by the amount of hydrogenconsumed. At the end of 93min'utes the'hy'drog'enation was 10 'per centcompleted. After two" hours the rate ofhydrogenation began to'increasefrom about 6 percent per hour until at the end of about ensure itreached its maximum of about 32 per cent "per hour. Thereafter, the ratedropped as the re' action approached completionuntil fl'rially thehydrogenation' stopped." The product was sub stantially purephenylmethyl carbinol obtained in almost quantitative yield.

In comparison with the foregoing results, a copper oxide-chromium oxidecatalyst which the metals were present in the ratio of 2.7 partschromium to 100" parts copper, by weight, re quired 2 hours forthe'hydrogenation to progress to the extentof 1 0 per cent, using thesamehyP drogenating procedure of this example, The maximum hydrogenationrate of this low' chromium catalyst was only 18 per cent per hour,"which was reached after 5.5hour's. In preparing this low' chromiumcatalyst, the'procedure described in Example lwas followed usingf2 88'grams of copper nitrate trihydrat'ej "13, gramsof chromium nitratemonoh'ydrate 'and grams of ammonium carbonateimoriohydrate. The meant,of catalyst obtainedwas 8 2"grams. No nnprov merit in themaximumtrodueuan rate resulted, upon subjecting'th low chromium' cassete the same treatment which wassuejcess'ru11ye1n: ployed toactivatecatalysts havingafhigh'r chromium-copper ratio (see Example '3),al though some slight improvementwas shown in the time of/iminutes'reduired for the hydro? genation to proceedlllfper 'c'ent;

Eaample 3 formed, until it had reached about 140 C. The entire heatingperiod was about one hour. The black mixed oxides were then recovered byfiltering, and washed with acetone. There was obtained about 4.6 gramsof non-pyrophroic activated catalyst. Example 4 To 100 parts by weightof pure acetophenone, contained in a suitable reaction vessel, was added2 parts by weight of the non-pyrophoric activated catalyst prepared asdescribed in Example 3. The mixture was then heated to about 130 0., andhydrogen introduced into the heated mixture under an average pressure ofabout 75 pounds per square inch while the mixture was being agitated,all precisely as described in Example 2. The catalyst wasactive from thestart and the hydrogenation was per cent completed at the end of 17minutes in comparison with the 93 minutes required to reach 10 per centusing the unactivated catalyst. The hydrogenation, using the activatedcatalyst reached its maximum rate of 43 per cent per hour after minutesand this rate was maintained until the hydrogenation was almostcomplete. Substantially pure phenyl methyl carbinol was obtained inpractically quantitative yield.

Example 5 Cr (N03) 3 9H2O in 2 liters of water. The stirring wascontinued 20 minutes after the addition had been completed. Aprecipitate formed, which was a mix- 7 ture of thecopper carbonate andchromium carbonate, and from this point on the treatment of theprecipitate was according to the procedure described in Example 1. Therewas obtained 4'? grams of black mixed oxides in which the metals werepresent in the proportion of 9.8 parts chromium to 100 parts copper, byweight.

A part of the black mixed oxides thus obtained was activated accordingto the procedure of Example 3 to yield a non-pyrophoric activatedcatalyst withabout the same activity as described in Example 4.

Example 6 A mixed oxides catalyst containing copper and chromium in theproportion of 23 parts chromium to 100 parts copper, by weight, wasprepared by the method described in Example 1, using 212 grams of coppernitrate trihydrate, 79 grams of chromium nitrate monohydrate and 170grams of ammonium carbonate monohydrate. The resulting black mixed oxidecatalyst thus obtained was slightly less active than the catalyst ofExample 1. Under the same conditions as described in Example 2, 100minutes were required to attain 10 per cent hydrogenation, as against 93minutes for the black mixed oxides having a chromium-copper ratio of13.8 parts chromium to 100 parts copper, by weight.

Example 7 A part of the black mixed oxides catalyst of Example 6containing copper and chromium in the ratio of 23 parts chromium to 100parts copper by weight was activated by the procedure dropped ofisharply to one per cent per hour as theyhydrogenation reaction nearedcompletion. The activated catalyst wa not pyrophoric.

Example 8 Black mixed oxides catalyst, prepared as described inExample 1and containing copper and chromium in the ratio of 13.8 parts chromiumto parts copper, by weight, was heated by. placing it in a U-tube whichwas, in turn, immersed in an oil bath. The oil bath was maintained at atemperature of 160 C. and hydrogen passed'slowly through the tube forsix hours. During the firsttwo hour water was produced. The catalystthus activated was found to be pyrophoric and consequently wasdischarged directly from the tube, after cooling, into anacetophenonephenyl methyl carbinol mixture containing 79 per cent ofacetophenone. This mixture, containing 5 parts catalyst to 100 partsmixture, was hydrogenated at a temperature of 150 C. and under ahydrogen pressure of to pounds per square inch. At the end of 2.75 hoursthe phenyl methyl carbinol content of the mixture had been increased to94 per cent, by weight.

Example 9 Black mixed oxides catalyst made by the method of Example 1and containing copper and chromium in the proportion of 100 parts copperto 13.8 parts chromium, was mixed with dry ethyl benzene in the ratio of10 parts catalyst to 360 parts ethyl benzene. The mixture was thenheated in a pressure reactor to a temperature of 150 C. and hydrogenintroduced under a pressure of 60 to 65 pounds per square inch. Thepressure wa released at one-half hourly intervals to allow the hydrogento sweep out the small amount of water formed in the partial reductionof the catalyst, and again restored by the introduction of hydrogen. Atthe end of three hours the catalyst was recovered by filtration andwashed with acetone. The catalyst, thus activated, was found to benon-pyrophoric.

To 200 grams of a mixture containing 73 per cent acetophenone and 27 percent phenyl methyl carbinol in a pressure reactor was added 8 grams ofthe activated catalyst. The acetophenonecarbinol-catalyst mixture wasthen maintained at an average temperature of 142 0., and hydrogenintroduced at a pressure of 100 to 150 pounds per square inch. In threehours the concentration of phenyl methyl carbinol reached 98 per cent,by weight.

Example 10 Acetophenone was hydrogenated to phenyl methyl carbinolcontinuously as follows:

- plioduction rate was 0.55; and 0.37: partoi: methyl. carbinol per.part of. acetophenone. teed per. hour, by weight, forruns A and B, re.-,Spectiy y. Th temperature. was maintained at k510i: 0-. and the pressureat L50ipounds per square, inch, for both runs. The. catakzstused was,pref. paredraccording. to. Example, 9;, and: the. average; catalyst,concentration, during. both runs; was about 2 per cent, bygneight, ofthe reaction mixture.

The. invention susceptible. of modification within. the scope. of theappended claims.

. This. application is a. division. at .ourr copending application.filed. October... 14, 1943, Serial No." 506,214, noiaU. S. Patent2,544,771 issued March ll-3. 1951..

Weclaim: Y

11 Theimprovement of the art othydrogenating acetophenona which consistsin producing phenyl methyl carbinol to the substantialex.- clusion. ofethyl benzene or other sidereaction products by carryingoutthehydrogenation undera hydrogen pressure of about 50 to 200 pounds pers'quar'einch, gage, anda temperature of about 20 to 209 C. 'in'thepresence of a catalytic amount of a copper-chromium mixed oxideshydrogenatiqn catalyst in which chromium is present inaratioicornputedon a metal basis, from about 'ito '25 parts of chrqmiurnper; lilo-parts of j copperby'weight'i 2. The improvement of-therart ofhydrogenating, ace tophenone which consists in producing pli n l he hicarh no o the sub ta e t ion. it ethyl htn fiee t' h sid macaw nature;b rr in cut... h yd on un e ahydmgert essu e of; t. 1 to F150 pnfdsfrze'r square inch, gage, and a te nperature ohtflSOf to 175i C.inthe presence of a cat-.

amount of a copper-chromium mixed hyd cs at oncatalyst i wh chchro l f't in a ratio computed on a metal basis, froinabout 7 to parts ofchromium per 100 are f narh i h 31.1 TheQirnp-rove'mentof,the art ofhydrogenat ingsl acetpphenone which. consistsin producing piie'nylmethyl carbinoi to the substantial ex.-

h Q5] hyl e e th r ide e im.

products by carrying out the hydrogenation .unde r a. ydr en,- ers sxmiye e -'0 s. 0 p td per square inch, gage, and a temperature-0t about120? to. 200 C, in the presence. of a catalytic amount of: acopper-chromium mixed oxides hydrogenation catalyst in which chromium ispresent in a ratio computed ona metal: basis, fromabout 9 to 15 parts ofchromium perparts of copper by weight.

4, Theimproyement of theart of hydrogenating. acetophenone whichconsists in producing: phenyl methyl carbinol to, the substantialeggclusion of ethyl benzene. or other side reaction-. Pr du ts by r yino eh d eenati c under; h r e es ur f: ab ut. ound per squar'einch, gage,and atemp erature-of about;

13Q- to 1755' C. in the presence. of a catalytic;

mq nt of c h mium mixed oXideshy-e drog enation catalyst in whichchromium-isll iflsent in a ratio; computed on ametal basis, from about 91M 5 um perwQ ar sQi; copper by weight.

5. The improvement oftheart of hydrogenat ing acetophenone whichconsists in producing phenyl methyl, carbinol' to the substantial; eX--catalyst in which chromium is ,present, in a ratio of: about 13.8 partsper 100 parts of copper-, by weight, computed on a metal basis.

DONALD M, YOUNG.

FRANK G. YOUNG, JR} 1 HOWARD R. GUEST."

REFERENCES CITED The following references are-of record in the file ofthis patent:

Maw z kf a Apr. 1-..19431-

1. THE IMPROVMENT OF THE ART OF HYDROGENATING ACETOPHENONE WHICHCONSISTS IN PRODUCING PHENYL METHYL CARBINOL TO THE SUBSTANTIALEXCLUSION OF ETHYL BENZENE OR OTHER SIDE REACTION PRODUCTS BY CARRYINGOUT THE HYDROGENATION UNDER A HYDROGEN PRESSURE OF ABOUT 50 TO 200POUNDS PER SQUARE INCH, GAGE, AND A TEMPERATURE OF ABOUT 120* TO 200* C.IN THE PRESENCE OF A CATALYTIC AMOUNT OF A COPPER-CHROMIUM MIXED OXIDESHYDROGENATION CATALYST IN WHICH CHROMIUM IS PRESENTIN A RATIO COMPUTEDON A METAL BASIS, FROM ABOUT 7 TO 25 PARTS OF CHROMIUM PER 100 PARTS OFCOPPER BY WEIGHT.